I wouldn't worry about it - if someone you interviewed with was staunchly anti-bitcoin, you could certainly claim you did it as you found it an interesting tech

I wouldn't worry about it - if someone you interviewed with was staunchly anti-bitcoin, you could certainly claim you did it as you found it an interesting technical problem rather than being a "true believer". But I suspect most people who are skeptical of bitcoin as a viable currency still think it's kind of neat technically, and would be impressed at you writing some (presumably good) code for it.